It is certainly a weird issue.
I can't see how org-mode would behave differently at the OS level from other emacs package bindings. Likewise, there is nothing different or unusual about how org-mode does key bindings. If there was a problem at the OS, window manager or interface library (i.e. gtk) level, it should affect all bindings.
I'm sure this has been checked, but make sure it isn't the window manager/OS 'stealing' the keys. When I install emacs on any system, the first thing I do is use the OS or window manager facilities to remove/disable any OS/window manager shortcuts so that the key presses get passed through to Emacs. I doubt this is the problem because if it was, you would see the same issue iwth other Emacs modes/packages, not just org-mode.
Unless someone can produce a minimum example which can reproduce this issue, I don't even see where to start.
I shold have mentioned that the version of Ubuntu I use is Gnome and I build emacs with GTK.
I should also mention that Ubuntu (well Debian really) install a versino of emacs which is customized and not stock-stnadard emacs. Also, my macOS version of emcs is built using brew install and not brew cask install, so it is built from the git repo and not using the macforosx binaries the cask version uses.
Tim